Semiconductor integrated circuits are comprised of a multiplicity of circuit blocks, each containing various circuit components. A multiplicity of conductive lines connect the circuit components and circuit blocks to other circuit elements, as well as to each other. Generally speaking, each circuit component and circuit block includes a highly integrated, densely packed multitude of individual features. Each individual circuit block occupies a significant amount of surface area within the semiconductor substrate on which the integrated circuit device is formed. The conductive lines which connect the circuit components and circuit blocks to each other and to other circuit elements, including external features, do not require significant surface area. When a conductive line which is formed to access a circuit component, is non-operational, then the individual circuit component cannot be accessed and is rendered useless. When a conductive line for accessing an entire circuit block is non-operational, the entire circuit block cannot be accessed and is therefore useless. When this occurs, a significant amount of the surface area which forms the integrated circuit is wasted.
Conductive lines are typically formed of metals such as copper, aluminum, or their alloys, and are generally relatively long lines which may surround or traverse a number of circuit blocks within an integrated circuit device. Relative to the features within a circuit block, the conductive lines are of considerably greater length because they connect the individual circuit blocks to any number of relatively remote components within the integrated circuit device. For example, in a random access memory (RAM) or a read only memory (ROM) device, the individual circuit components may be storage cells for a memory device. The storage cells for a memory device may be arranged in an array consisting of horizontal rows and vertical columns. Such an array may be considered a circuit block. In this configuration, each cell shares electrical connections with all the other cells in its row, and column. The electrical connections are provided by conductive data lines that may include horizontal lines connected to all the cells within a row, which are called word lines, and also vertical lines (along which data flows into and out of the cells), which are called bit lines. When the conductive data line that connects a memory cell to another component is defective, the memory cell is useless.
To address the problem associated with defective metal conductive lines, one approach may be to provide additional circuit components, for example: extra memory cells in a DRAM device. Using this approach, both an extra memory cell and an associated conductive data line must be provided. However, active circuit components such as a memory cell can require a considerable amount of surface area within the semiconductor substrate. As such, providing additional circuit components within a semiconductor integrated circuit device comes at the expense of providing a device of significantly reduced size. This is undesirable, as it allows for a lesser number of integrated circuit devices to be formed simultaneously within a substrate of fixed dimension (e.g. a six inch wafer). As such, adding additional circuit components to a semiconductor integrated circuit device may not be a cost-effective method for increasing yield.
As the number of levels of device hierarchy within an integrated circuit device increases, so, too does the deleterious effect of a non-functioning conductive line. For example, with respect to the DRAM device described above, when a read-write line is defective, then all of the individual memory cells which constitute an array or circuit block, and are connected by way of a bit line to the defective or non-operational read-write line, are rendered useless. To guard against the possibility that a read-write line may be defective, an additional multiplicity of cells which form the array, would be required. From this example it can be understood that providing spare circuit blocks or components in order to compensate for a potentially defective conductive line, is not always practical.